percentage depletion

depletion allowance

...was enacted in 1918 to stimulate oil production for World War I (even though the war had just ended). Discovery value proved too hard to estimate, however, so this was changed in 1926 to the “percentage depletion” for oil and gas property, under which the corporation deducts a fixed percentage of its sales as a depletion allowance, regardless of the amount invested. In...